A projector, which achieves a large screen display by projecting an enlarged image onto a screen, has conventionally been known as a projection image display apparatus. Recently, in particular, a so-called liquid crystal projector, which optically modulates light emitted from a light source by using a liquid crystal display device and projects the light onto a screen, has become widespread. The liquid crystal display device displays an image in a display mode corresponding to the type of liquid crystal molecules used in a liquid crystal panel.
For example, a liquid crystal display device operating in a vertical aligned (VA) mode, in which liquid crystal molecules that have negative dielectric anisotropy are filled in the gap between a pair of substrates included in a liquid crystal panel so as to distribute light vertically, is well known. In the VA-mode liquid crystal display device, because the liquid crystal molecules are aligned substantially perpendicular to a main plane of each of the substrates when no electric field is applied, light passes through a liquid crystal layer substantially without changing a plane of polarization thereof. Therefore, arranging a polarizer on each of the top and the bottom of the substrates enables the black to be satisfactorily displayed when no electric field is applied. In contrast, when an electric field is applied, the liquid crystal molecules are aligned obliquely with respect to the main plane of the substrate, and resultant birefringence rotates the plane of polarization of incident light. Compared with a liquid crystal display device operating in a twisted nematic (TN) mode, the VA-mode liquid crystal display device has an advantage of realizing a higher contrast ratio.
The VA-mode liquid crystal display device obtains birefringence by obliquely aligning liquid crystal molecules during an application of an electric field. Therefore, when no electric field is applied, the liquid crystal molecules are aligned at a minute tilt angle (pretilt angle) in advance. Since the liquid crystal molecules are not completely perpendicular and are slightly oblique with respect to a main plane of a substrate when no electric field is applied, residual retardation occurs in a liquid crystal panel. As a result, a plane of polarization of normal incident light is rotated slightly, thus causing light leakage from a polarizer and thereby decreasing a contrast.
Additionally, in the VA-mode liquid crystal display device, when no electric field is applied, retardation is introduced with respect to oblique incident light. Therefore, if a cone angle of incident light is increased (F# is reduced) to acquire a high intensity (brightness), the contrast is decreased.
A projection image display apparatus, such as a three-panel liquid crystal display projector which has three liquid crystal panels corresponding to three colors (RGB), is known. The projection image display apparatus generally uses a prism-type polarization beam splitter (PBS) to perform polarization separation. However, the prism-type PBS has a large angular dependency, causing a decrease in the contrast. If the cone angle is limited in order to maintain an adequate contrast, it is disadvantageous in terms of the intensity (brightness).
To address this, a technique is proposed in which a decrease in the contrast caused by a prism-type PBS is reduced by placing a quarter wave plate between a liquid crystal panel and a polarizing plate (see Japanese Patent No. 3019813).
A method is suggested that uses a combination of a wire grid polarizer which has a small angular dependency, instead of the prism-type PBS, a reflective liquid crystal panel, and a retardation plate for compensating for the residual retardation caused by pretilting in the liquid crystal panel and for retardation with respect to oblique light (see Japanese Unexamined Patent Application Publication No. 2005-18071).
Japanese Unexamined Patent Application Publication No. 2000-227520 discloses a technique for producing a retardation plate by using a combination of two or more kinds of retardation films having different refractive properties.